Hydrodynamic bearing runner for use in tilting pad thrust bearing assemblies for electric submersible pumps

ABSTRACT

An electrical submersible pump runner having a core layer and a wear layer affixed to the core layer. One embodiment of the invention provides an electrical submersible pump that includes a motor section and a centrifugal pump section. A seal section and rotary gas separator may also be included. The pump is powered by an electric cable that connects the pump, located in a bore hole, to a power source on the surface. A thrust runner coated with a wear layer (e.g., polymer) is provided in the motor and/or seal section to reduce bearing temperature, provide longer bearing life, reduce costs, and facilitate overhaul. The runner may also function as a rotating up-thrust bearing when the runner is coated with a wear layer on one side that is formed with a bearing geometry. In this case, the up-thrust bearing may be eliminated.

This application claims the benefit of U.S. Provisional Application Ser.No. 60/474,298, filed May 30, 2003, and U.S. Provisional ApplicationSer. No. 60/480,744, filed Jun. 24, 2003, which are both incorporatedherein by reference in their entirety.

BACKGROUND

1. Field of the Invention

This invention relates to electrical submersible pumps, and moreparticularly to electrical submersible pumps that are powered by anelectrical cable and have hydrodynamic (fluid film) thrust bearings intheir motor section and in their seal section when employed.

2. Background of the Invention

Electric submersible pumps are used to lift liquids such as oil, water,or brine. They are typically long relative to their diameter to fit downdrilled holes. For deep wells, a typical pump system consists of amulti-stage centrifugal pump, rotary gas separator, seal section, andmotor. The motor is connected to an electric power source at the surfacevia electric cables. The rotor in the electric motor incorporates atilting-pad hydrodynamic (fluid film) thrust bearing to support therotor weight. The seal section prevents external well fluids fromentering the motor and equalizes the pressure between the well fluid andinternal motor lubrication oil. The seal section also houses up and downhydrodynamic tilting pad thrust bearings to react loads developed by thecentrifugal pump.

For shallow wells such as those used to pump water from drilled holesfor potable water, the seal and gas separator sections are eliminated.Tilting pad bearings are still used in the motor section.

For both deep and shallow well pumps, it is industry practice tomanufacture the bearing pads of a relatively soft material and run themagainst a harder runner.

FIG. 5 illustrates the seal section portion of a known deep wellsubmersible pumping system, produced by Baker Hughes of Houston, Tex.under the name Centrilift™. As shown, this seal section of thesubmersible pumping system includes a runner 550 between a down-thrustbearing 552 and an up-thrust bearing 554.

Tilting pad type hydrodynamic thrust bearings are also known from thepresent inventor's previous U.S. Pat. No. 4,676,668 to Ide, U.S. Pat.No. 5,137,373 to Ide, and U.S. Pat. No. 5,125,754 also to Ide, which areincorporated herein by reference in their entirety. In U.S. Pat. No.5,137,373, the bearing can be formed in a single piece; in the other twopatents, individual bearing pads are supported in a separate carrier.

In the context of a hydrodynamic thrust bearing, the stationary bearingpads face a rotating “runner” that is secured to (e.g., as by a key) orintegrally formed with a shaft, in the presence of a lubricant(typically oil, but also water or a “process fluid”), which effectivelyseparates the two components of the system via an elevated pressuredeveloped at the interface as a result of hydrodynamic effects. Forelectric submersible pump seal sections, the direction of loading may bein two opposite directions. Hydrodynamic bearings are therefore spacedon both sides of the rotating runner.

In the prior art bearing/runner assemblies described in theaforementioned patents, the pads and runners are fabricated fromdissimilar materials to preclude galling should the two components comeinto contact while under load (particularly at start-up, but also duringoverload conditions while running). In practice, the pads are, forexample, either monolithic bronze, carbon, or fabricated from steelcoated with a relatively “soft” non-ferrous material on the runningsurface, while the runners are typically hardened steel. Among thecoatings used are engineered plastics. Industry practice is to apply thevarious coatings to the bearing pads.

SUMMARY OF THE INVENTION

In accordance with the present invention and contrary to the industrypractice of applying the various coatings to the bearing pads, thepresent inventor has discovered that, in the case of engineered plasticcoatings, commercial and performance advantages result from applying thecoating to the runner rather than the pads. The pads are preferablyuncoated hardened steel. The unexpected advantages resulting from theconstruction of the present invention include:

-   -   Only one component (i.e., the runner) of the bearing/runner        assembly is coated, rather than coating multiple components        (i.e., the pads, of which there are typically 5 to 10 per        assembly); this results in lower cost (including lower waste of        plastic in the molding process).    -   The swept area of wear surface (i.e., plastic) is larger with        the runner coated and thus the wear rate under mixed/boundary        lubrication conditions is reduced, increasing bearing/runner        longevity.    -   The swept area of wear surface (i.e., plastic) is larger with        the runner coated and thus the surface temperature under        mixed/boundary lubrication conditions is reduced, increasing        bearing/runner longevity.    -   The bearing pads, when made of hardened steel, eliminate pad        wear. The less costly runner becomes the sacrificial component.        Since only the runner may need replacement, overhauls are less        complex and costly.    -   Recoating individual pads is not practical or economical;        recoating a runner is both economical and readily accomplished.    -   Conventional uncoated runners may be re-ground/re-lapped if the        design thickness tolerance permits, but plastic-coated runners        may be reworked indefinitely since only the worn plastic/bronze        interlayer is removed and replaced (the steel substrate remains        intact in the process).    -   The coating on one or both sides of the runner may be applied to        form a hydrodynamic bearing pad that rotates with the runner. In        this case, the rotating runner actually becomes the bearing and        the stationary “bearing” can be replaced by a simple flat plate.        In submersible pumps, this can provide a significant advantage.        In the pump bearing arrangement, the lower bearing normally        reacts operating loads while the upper bearing reacts transient        startup up-thrust loads only. By incorporating bearing pads on        the runner, the up-thrust bearing can be eliminated.

Thus, an embodiment of the present invention provides an electricalsubmersible pump shaft and bearing combination including a generallycylindrical shaft having a runner formed or secured thereon. Inaccordance with an important aspect of the invention, the runner that issupported by the bearing pads is provided with a surface layer ofengineered plastic such as polyimide or other polymer coatings. As usedherein, an engineered plastic refers to a plastic (e.g., polymer) havinghigh performance characteristics such as high strength, high temperaturecapability, chemical resistance, and heat resistance. The plastic isengineered to provide the properties required for a particularapplication. Additional materials can also be added to provide othermaterial characteristics, such as adding Teflon™ and/or graphite toreduce coefficients of friction. Examples of engineered plastics includepolyimide, PEEK, nylon, PTFE, and polyamid-imide. Naturally, othermaterials may be used, provided that the chosen material has therequired support and wear characteristics. In the currently preferredembodiment, an engineered plastic layer such as polyimide is provided ona sintered bronze layer.

Applying the bronze layer and the polyimide layer to the runner yieldsadvantages similar to those achieved in prior art bearing/runnerassemblies in which engineered plastic coatings are applied to thebearing pads. In particular, the plastic layer provides a wear surfaceso as to avoid damage to the pad during start-up. The wear surfaceallows the pad to withstand wear caused during start-up. By providing awear surface, the bearing assembly operates in two modes. First, atinitial start-up, the bearing assembly acts as a wear bearing whereinthe coated runner shaft rubs against the pad surface. After start-up,the bearing assembly operates hydrodynamically and there is little or nocontact between the shaft and bearing pad surface.

Importantly, however, applying the bronze layer and the polyimide layerto the runner yields advantages beyond those of prior art bearing/runnerassemblies in which engineered plastic coatings are applied to thebearing pads. To begin with, coating a runner is cheaper than coatingbearing pads. In addition, the bearing pads may be constructed ofhardened steel, which in turn prolongs their life. Thus, the moreexpensive component of the bearing/runner system is constructed with thelongest life and the cheaper item of the two is constructed as areplaceable wear item. Also, the runner is a much simpler component(e.g., a disc), thus allowing for fairly simple retrofitting to existingsystems. Normally, runners are manufactured of heat-treated and oftenexpensive materials. By using such a polymer coating, the runner itselfmay be manufactured of less expensive, and more easily machined mildsteel.

Another advantage of the present invention is that the steel substratecan conduct heat away from the polymer (considered an insulator) betterthan a conventional polymer-coated bearing pad due to the greatersurface area of the runner in comparison with the surface area of thebearing pad(s). Also, by coating the runner, there is more polymersurface area to wear than if the pads themselves are coated. This mayextend the bearing/runner life when mixed lubrication occurs. For thecase where the coating forms a hydrodynamic bearing pad on the runnersurface, one of the pump bearings can be eliminated.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial sectional view of a runner according to an exemplaryembodiment of the present invention.

FIG. 2 is a sectional view of the runner of FIG. 1 in combination with ashaft and bearing assembly.

FIG. 3 is a partial sectional view of a runner with hydrodynamic bearingpads on one side, according to an embodiment of the present invention.

FIG. 4 is a plan view of the runner of FIG. 3 showing the bearing padson the runner face.

FIG. 5 is a sectional view of a seal section portion of a prior art deepwell submersible pumping system.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of thrust bearing runners are described in this detaileddescription of the invention. In this detailed description, for purposesof explanation, numerous specific details are set forth to provide athorough understanding of embodiments of the present invention. Oneskilled in the art will appreciate, however, that embodiments of thepresent invention may be practiced without these specific details. Inother instances, structures and devices are shown in block diagram form.Furthermore, one skilled in the art can readily appreciate that thespecific sequences in which methods are presented and performed areillustrative and it is contemplated that the sequences can be varied andstill remain within the spirit and scope of embodiments of the presentinvention.

In an embodiment of the present invention, FIG. 1 shows a bi-directionalrunner 100 having a bronze layer 102 (e.g., sintered bronze layer) and awear layer 104 (e.g., made of an engineered plastic such as polyimide).In this example, runner 100 is a keyed steel runner with copperelectroplating. Although runner 100 is depicted as a bi-directionalrunner, it is also possible to construct a uni-directional runner havingthe bronze layer 102 and layer 104 only on one side. In prior artbearing/runner assemblies, engineered plastic coatings may be used ontilt pad thrust bearings, but the plastic has invariably been applied tothe bearing pads. By applying the bronze layer 102 and layer 104 to therunner, many advantages may be achieved.

To achieve this construction, runner 100, which may be a core layer madeof steel, for example, is plated with a copper alloy. Runner 100 thenhas the porous bronze layer 102 added, for example, in a sinteringprocess. After bronze layer 102 is in place on runner 100, layer 104 maybe added, for example, by an injection molding process. In this manner,the material of layer 104 (e.g., polyimide) may flow into the porousareas of bronze layer 102, thus creating a wear surface firmly anchoredto runner 100. In addition to polyimide, layer 104 may be made of othermaterials having suitable PV (pressure-times-velocity) values, such aspolysultone and polyphenylene sulfide. Materials with a high PV valuecan withstand higher loads and higher speeds those with a lower PVvalue. In addition to injection molding, layer 104 may be affixed torunner 100 by other means, such as mechanical fastening or adhesives.

Applying the bronze layer and the polyimide layer to the runner yieldsfunctional advantages similar to those achieved in prior artbearing/runner assemblies in which engineered plastic coatings areapplied to the bearing pads. In particular, the plastic layer provides awear surface so as to avoid damage to the pad during start-up. The wearsurface allows the pad to withstand wear caused during start-up. Evenwith a relatively rigid support structure, the assembly can be designedto achieve hydrodynamic operation during steady state conditions, butthe wear characteristics at start-up can cause a potential concern. Byproviding a wear surface, the bearing assembly operates in two modes.First, at initial start-up, the bearing assembly acts as a wear bearing,wherein the coated runner shaft rubs against the pad surface. Afterstart-up, the bearing assembly operates hydrodynamically, and there islittle or no contact between the shaft and bearing pad surface.

By affixing the wear layer 104 to runner 100 rather than the bearingpads, further significant advantages may be achieved. For example,coating a runner is cheaper than coating bearing pads. In addition, thebearing pads may be constructed of hardened steel, which in turnprolongs their lives. Thus, the more expensive component of thebearing/runner system is constructed with the longest life and thecheaper item of the two is constructed as a replaceable wear item. Also,the runner is a much simpler component (e.g., a disc), thus allowing forfairly simple retrofitting to existing systems. Normally, runners aremanufactured of heat-treated and often expensive materials. By usingsuch a polymer coating, the runner itself may be manufactured of lessexpensive, and more easily machined mild steel.

Another advantage of the present invention is that the steel substratemay conduct heat away from the polymer (considered an insulator) betterthan a conventional polymer-coated bearing pad, due to the greatersurface area of runner 1100 in comparison with the surface area of thebearing pad(s). Also, by coating runner 100, there is more polymersurface area to wear than if the pads themselves are coated. This mayextend the bearing/runner life when mixed lubrication occurs.

FIG. 2 depicts runner 100 in combination with bearing pads 300 and ashaft 200, according to an embodiment of the present invention havingbi-directional up and down thrust. In this example, runner 100 is akeyed steel runner with copper electroplating.

FIG. 3 shows a runner 400 on which bearing pads 401 are molded on oneside of the runner 400, according to an embodiment of the presentinvention. Holes or passageways 402 connect the pads 401 to the runnersurface 403 so that the plastic can be injection molded in oneoperation. The holes 402, as well as undercuts 404, provide mechanicallocks to hold the plastic of pads 401 and surface 403 in position.Optionally, instead of holes or undercuts, simple recesses or cavitiescould be provided in the surface of runner 400 into which plastic couldbe molded to form the pads 401. The bearing 500 is shown as a simpleplate. FIG. 4 shows the runner 400 and bearing pads 401 in plan view.

The foregoing disclosure of the preferred embodiments of the presentinvention has been presented for purposes of illustration anddescription. It is not intended to be exhaustive or to limit theinvention to the precise forms disclosed. Many variations andmodifications of the embodiments described herein will be apparent toone of ordinary skill in the art in light of the above disclosure. Thescope of the invention is to be defined only by the claims appendedhereto, and by their equivalents.

Further, in describing representative embodiments of the presentinvention, the specification may have presented the method and/orprocess of the present invention as a particular sequence of steps.However, to the extent that the method or process does not rely on theparticular order of steps set forth herein, the method or process shouldnot be limited to the particular sequence of steps described. As one ofordinary skill in the art would appreciate, other sequences of steps maybe possible. Therefore, the particular order of the steps set forth inthe specification should not be construed as limitations on the claims.In addition, the claims directed to the method and/or process of thepresent invention should not be limited to the performance of theirsteps in the order written, and one skilled in the art can readilyappreciate that the sequences may be varied and still remain within thespirit and scope of the present invention.

1. A electrical submersible pump runner for use in a pad-typehydrodynamic bearing/runner assembly, the runner comprising: a corelayer; a wear layer affixed to the core layer, wherein the wear layer isa first polymer layer, and wherein the runner further comprises a secondpolymer layer affixed to the core layer on a side of the runner oppositethe first polymer layer, and wherein the core layer defines a passagewaythrough which the first polymer layer and the second polymer layer areconnected.
 2. The runner of claim 1, further comprising at least oneporous bronze layer affixed to the core layer, wherein the wear layer isaffixed to the core layer by being affixed to the at least one porousbronze layer.
 3. The runner of claim 1, further comprising first andsecond porous bronze layers affixed to opposite sides of the core layerto which respective ones of the first and second polymer layers areaffixed.
 4. The runner of claim 1, wherein the core layer comprises mildsteel.
 5. The runner of claim 1, wherein the core layer comprises copperelectroplating.
 6. The runner of claim 1, wherein the wear layercomprises polyimide.
 7. The runner of claim 1, wherein the core layerdefines a recess in which the wear layer is disposed.
 8. The runner ofclaim 7, wherein the recess comprises an undercut.
 9. The runner ofclaim 7, wherein the wear layer protrudes from the recess above the corelayer.
 10. The runner of claim 1, wherein the core layer defines arecess in which the first polymer layer is disposed.
 11. The runner ofclaim 10, wherein the recess comprises an undercut.
 12. The runner ofclaim 1, further comprising a porous bronze layer affixed to the corelayer on the side of the runner opposite the first polymer layer,wherein the second polymer layer is affixed to the core layer by beingaffixed to the porous bronze layer.
 13. A runner for use in a pad-typehydrodynamic bearing/runner assembly, the runner comprising: a corelayer; and a polymer layer affixed to the core layer, wherein thepolymer layer forms a plurality of spaced bearing pads to provide abearing that rotates with the runner.
 14. The runner of claim 13,wherein the core layer defines recesses into which the polymer layer ismolded.
 15. The runner of claim 14, wherein the recesses compriseundercuts.
 16. A bearing and runner assembly for use in a submersiblepump system comprising: a bearing comprising at least one bearing pad;and a runner comprising a polymer coating affixed to a first side of therunner and individual bearing pads on a side of the runner opposite thefirst side.
 17. The assembly of claim 16, wherein the runner definespassageways through which the polymer coating is connected to theindividual bearing pads.
 18. The assembly of claim 16, wherein therunner defines recesses in which the individual bearing pads aredisposed, and wherein the recesses comprise undercuts.
 19. The assemblyof claim 16, wherein the runner further comprises a porous bronze layerto which the polymer coating is affixed.
 20. The assembly of claim 16,wherein the bearing comprises uncoated hardened steel.
 21. A submersiblepump system comprising: a multi-stage centrifugal pump; and a motorcoupled to the multi-stage centrifugal pump, the motor comprising: ashaft coupled to the multi-stage centrifugal pump, a rotor having athrust bearing, and a first runner affixed to the shaft, the runnercomprising a first core layer and a first wear layer affixed to thefirst core layer, wherein the first wear layer faces the thrust bearing;further comprising a rotary gas separator and a seal section, whereinthe shaft extends through the seal section, and wherein the seal sectioncomprises: an up-thrust plate, a down-thrust bearing, and a secondrunner affixed to the shaft and disposed between the up-thrust plate andthe down-thrust bearing, wherein the second runner comprises: a secondcore layer, a second wear layer affixed to a first side of the secondrunner facing the up-thrust plate, and a third wear layer affixed to asecond side of the second runner facing the down-thrust bearing.
 22. Thesystem of claim 21, wherein the second runner defines recesses in whichthe second wear layer is disposed.
 23. The system of claim 21, whereinthe second layer comprises individual bearing pads.
 24. The system ofclaim 21, wherein the second runner defines a passageway through whichthe second wear layer is connected to the third wear layer.
 25. Asubmersible pump system comprising: a multi-stage centrifugal pump; anda motor coupled to the multi-stage centrifugal pump, the motorcomprising: a shaft coupled to the multi-stage centrifugal pump, a rotorhaving a thrust bearing, and a first runner affixed to the shaft, therunner comprising a first core layer and a first wear layer affixed tothe first core layer, wherein the first wear layer faces the thrustbearing; and wherein the first core layer comprises mild steel, thefirst wear layer comprises a polymer, and the thrust bearing comprisesuncoated hardened steel.
 26. A method for overhauling a submersible pumpsystem having a runner removably attached to a shaft, the methodcomprising: removing the runner from the shaft; removing a surface layerof the runner to expose a core substrate; applying a wear layer to thecore substrate; and reattaching the runner to the shaft.
 27. The methodof claim 26, wherein the surface layer comprises a worn polymer coating.28. The method of claim 26, wherein the wear layer comprises anengineered plastic.
 29. The method of claim 26, wherein applying a wearlayer to the core substrate comprises: applying a porous bronze layer tothe core substrate; and applying a polymer layer to the porous bronzelayer.
 30. The method of claim 29, wherein applying the porous bronzelayer comprises sintering the porous bronze layer.
 31. The method ofclaim 29, wherein applying the polymer layer comprises injection moldingthe polymer layer into porous areas of the porous bronze layer.
 32. Themethod of claim 29, wherein applying the polymer layer comprisesinjection molding the polymer layer into recesses of the runner to formindividual bearing pads.
 33. The method of claim 29, wherein applyingthe polymer layer comprises injection molding the polymer layer onopposite sides of the runner connected by passageways through therunner.